Each of the projector and the optical receiver of the multi-optical axis photoelectric sensor is configured such that an optical unit in which a plurality of optical elements are provided and a control board are accommodated in a rectangular-solid casing. Generally, in each casing, the front surface and both end surfaces of the frame body are opened, the end surfaces are closed by caps, respectively, and the opened front surface is interiorly closed by the light transmissive plate. A light transmission surface or a light receiving surface of the optical unit in the casing is oriented toward the opened front surface, whereby the opening of the front surface closed by the light transmissive plate acts as a window portion that transmits light.
Because this kind of sensor is possibly disposed in the field where dust and liquids fly, the caps at both ends are assembled in the frame body with rubber packings interposed therebetween. Similarly the light transmissive plate is fixed such that a gap is not formed between an opening edge of the frame body and the light transmissive plate.
For example, there is disclosed a light transmissive plate fixing method for coupling an end edge portion along the opening of the front surface of the frame body and the light transmissive plate using a double-sided adhesive tape (see paragraph number 0022 of Patent Document 1)). Sometimes a sealing agent having adhesion is used instead of the double-sided adhesive tape.
There is also a method in which a ring rubber is disposed between the opening and the light transmissive plate according to a shape of the opening and the light transmissive plate is fixed while being pressed by the rubber. Although the fixing method is directly disclosed, Patent Document 2 describes that a ring rubber is attached to an peripheral edge of the optical unit accommodated in the casing, the front surface of the frame body having the window portion is screwed while being pressed against the optical unit, and the front surface of the frame body is covered with the light transmissive plate (see paragraphs 0013 to 0016 and FIGS. 1 to 3 of Patent Document 2).
Additionally, there is proposed a method of FIG. 14 in consideration of a change in length of the frame body in each of the projector and the optical receiver according to an installation environment or a utilization purpose of the sensor.
FIG. 14 schematically illustrates a main configuration relating to sealing of the opening of the frame body. String-like rubbers 202 and 202 are interposed between a light transmissive plate 201 and both side edges of an opening of a front surface of a frame body 200, and plate-like rubbers 203 and 203 are disposed in an opening of both end surfaces. The light transmissive plate 201 is fixed while being sandwiched between a pressing member (not illustrated) and the string-like rubbers 202 and 202, the plate-like rubber 203 is fixed while being pressed against the end surface of the frame body 200 by a cap (not illustrated). At this point, a plate surface of the plate-like rubber 200 and the end edges of the string-like rubber 202 are brought into close contact with each other, and the opening of the frame body 200 can be sealed in a water-proof state.